The present invention relates generally to extrusion products and processes. The invention has particular application to a method of forming an ornamental enhancement integral with an extrusion profile. The resulting product has applications in the molding industry, including picture frames and door, wall and window moldings.
As a result of the increasing cost of wood and the attendant cost of detailing wood pieces for building construction, there exists a demand for alternatives to solid wood construction products. Accordingly, the use of plastic extrusion profiles as substitutes for wood products in the areas of picture frames and door, wall, and window moldings has increased significantly in recent years. Plastic extrusion processes of materials such as polyvinyl chloride (PVC) and polystyrene, for example, can provide a substitute for a wood picture frame or door or window molding.
While such plastic extrusions can provide a substitute for a wood product, the plastic extrusion may also need to be decorated with ornamental features to enhance the beauty and desirability of the ultimate product. Various types of designs and patterns, as well as paints and stains of various colors, are used to cover and otherwise decorate the plastic extrusion profile.
A conventional method for forming an ornamental feature on a plastic picture frame or molding is shown in UK Patent Application GB 2,276,318A to Robobond Ltd. of Great Britain. In the Robobond process, plastic frame members are extruded and cut into appropriate lengths. After the plastic extrusion cures and hardens, a solvent based wood paste is applied to the frame surface in such a manner that it forms an ornamentation on the surface of the length of plastic. The paste is then allowed to dry and the picture frame is assembled from the extrusion portions.
The Robobond patent teaches a preferred solvent based wood paste of toluene and acetone. The wood paste is etched into the plastic extrusion profile and enables the paste to form a resin bond with the polymer of the plastics material.
Several disadvantages exist with the Robobond process that make it undesirable for large-scale manufacturing. For example, the process requires a period of several days for the wood paste to dry, which is in addition to the time required for the extrusion profile to harden before application of the wood paste. Moreover, during the drying process, the wood paste causes a tension to be applied to the extrusion profile which results in upward bowing of the profile length. In order to counteract the bowing effect, the frames must be held in large drying racks. Finally, the wood paste is not easily applied and substantial amounts are wasted in the excess that is applied to the extrusion profile.
Such disadvantages in terms of time and excess equipment are very significant drawbacks in the effort to provide a low cost picture frame or other construction molding. The present invention attempts to overcome the above-described time and cost disadvantages in conventional ornamentation processes, such as the Robobond process.